{"id":98,"date":"2026-11-01T09:00:00","date_gmt":"2026-11-01T01:00:00","guid":{"rendered":"https:\/\/panovacuum.cn\/blog\/coating-chamber-cleaning-particle-control-en\/"},"modified":"2026-11-05T16:29:33","modified_gmt":"2026-11-05T08:29:33","slug":"coating-chamber-cleaning-particle-control-en","status":"publish","type":"post","link":"https:\/\/panovacuum.cn\/blog\/coating-chamber-cleaning-particle-control-en\/","title":{"rendered":"Why a coating chamber still will not pump down after cleaning"},"content":{"rendered":"

Nine times out of ten the problem is outgassing, not leakage. Two sources dominate: water, and hydrogen trapped in the damaged surface layer. Baking and pumping time address the first; only the cleaning process addresses the second.<\/p>\n

1. Water follows a simple empirical law<\/h2>\n

For all vacuum metals \u2014 stainless, copper, aluminium, titanium \u2014 room-temperature water outgassing is about 3\u00d710\u207b\u2079\/t (hours) in mbar\u00b7L\/(s\u00b7cm\u00b2). Ten times the pumping time gives one order lower outgassing and pressure. Two consequences: pumping longer is not folklore, and a cleaned chamber must be pumped immediately \u2014 a re-saturated water layer wastes the pumping already done.<\/p>\n

2. Baking fixes water, not hydrogen<\/h2>\n

Measured after 10 h pumping on stainless (Torr\u00b7L\/(s\u00b7cm\u00b2)): H\u2082O from 2\u00d710\u207b\u00b9\u2070 to 1\u00d710\u207b\u00b9\u2074, four orders; CO from 5\u00d710\u207b\u00b9\u00b2 to 1\u00d710\u207b\u00b9\u2074; H\u2082 from 7\u00d710\u207b\u00b9\u00b2 to 5\u00d710\u207b\u00b9\u00b3, barely one order and then flat. Hydrogen needs vacuum annealing or long pumping \u2014 the most commonly misread point when choosing a process route.<\/p>\n

\"White-cloth
Cleanliness verification: white-cloth wipe followed by visual judgement and particle counting.<\/figcaption><\/figure>\n

3. Baking temperature follows the material<\/h2>\n

Copper and aluminium reach below 10\u207b\u00b9\u00b3 with 150\u2013200 \u00b0C for 24 h; stainless needs above 200 \u00b0C, up to 300 \u00b0C, and millimetre-thick walls may need repeated bakes. In-situ baking above 120 \u00b0C for at least 12 h is effective on metal, with 150\u2013250 \u00b0C for 24 h as common practice, mainly for water. Viton is limited to about 200 \u00b0C; overheating deforms or decomposes it into a contamination source. This is why aluminium chambers bake easily and steel ones do not.<\/p>\n

4. Three criteria for ending a bake<\/h2>\n

Pressure stops falling at temperature; pressure returns to target after cooling; and the mass-18 (H\u2082O) peak drops below mass 28 (CO\/N\u2082) on the RGA. The first two are gauge readings; the third requires an RGA. Without one, calling a bake complete is guesswork.<\/p>\n

5. Cleaning has three layers, not one wipe<\/h2>\n

Grease, fingerprints and loose particles (solvents, alkaline detergent, ultrasound); oxide and contaminated films (acid, electropolish or chemical polish); and the damaged layer (vacuum annealing, ion bombardment). Skipping the third is the most common domestic shortfall: the surface looks clean, but hydrogen and impurities in the damaged layer bleed out, pressure stalls at 10\u207b\u2077 and baking cannot rescue it. A single bare-hand contact can outgas enough to cancel hours of baking.<\/p>\n

6. One O-ring costs two orders<\/h2>\n

A baked all-metal system reaches 10\u207b\u00b9\u2070\u201310\u207b\u00b9\u00b9 mbar ultimate; a single elastomer seal drops the ultimate to the 10\u207b\u2078 range. That is the quantitative basis for all-metal, CF-knife-edge construction in UHV \u2014 not a matter of taste.<\/p>\n

7. Check the vintage of any particle number<\/h2>\n

ITRS 2003 (FEP Table 70a): critical particle diameter 50 nm with 59 per wafer in 2003, 40 nm with 97 in 2005, 32.5 nm with 80 in 2007, 25 nm with 68 in 2009; critical GOI surface metals \u22640.5\u00d710\u00b9\u2070 atoms\/cm\u00b2, other critical metals \u22641\u00d710\u00b9\u2070, surface carbon 1.8\u00d710\u00b9\u00b3, mobile ions 1.8\u00d710\u00b9\u2070. This is the 2003 roadmap and today’s limits are tighter: the value lies in units, magnitude and definition, not as a current standard.<\/p>\n

8. Counter-intuitive: handling is dirtier than the chamber<\/h2>\n

ITRS 2003 Table 109a (defects\/m\u00b2, 54 nm equivalent): plasma etch 1049, CVD insulator 854, metal PVD 591, wet bench 474, CMP clean 397, while wafer handling is only 33, falling to 6 by 2009. Robots, lift pins and slit valves contribute more particles than the chamber itself \u2014 watching only the inner wall aims at the wrong target.<\/p>\n

9. 4 \u00c5 and Ra 0.1 \u00b5m are not the same thing<\/h2>\n

ITRS specifies LVGX RMS 4 \u00c5 (about 0.4 nm) on the wafer; domestic electropolishing commonly quotes Ra 0.1\u20130.2 \u00b5m, an industry rule of thumb. Two orders apart, and different definitions (RMS versus Ra). Neither equate electropolish Ra with wafer-level requirements nor condemn a chamber on Ra alone: gas flow, flow field and handling sit in between.<\/p>\n

10. Four rules that can be followed as written<\/h2>\n

Pump immediately after cleaning, never overnight in the shop; set bake temperature by material and keep Viton below 200 \u00b0C; end the bake on the three criteria, one of which must be the RGA 18\/28 comparison; finish with glow discharge cleaning where residual surface contamination matters. Cleaning is a process with criteria, not an action; an action without a criterion has not been performed.<\/p>\n

Outgassing and particles are separate problems: one is surface chemistry, the other is flow field and moving parts. Both need criteria, and criteria need to be reproducible.<\/p>\n

Frequently asked questions<\/h2>\n

The chamber was cleaned but still will not pump down \u2014 what first?<\/h3>\n

Separate outgassing from leakage first. Water-vapour outgassing decays as roughly 3\u00d710\u207b\u2079\/t per hour; if the surface water layer has re-saturated after cleaning, the pump-down time already spent is wasted.<\/p>\n

How much does baking solve?<\/h3>\n

Baking at 250 \u00b0C for 24 h pulls water vapour down about four orders of magnitude (2\u00d710\u207b\u00b9\u2070 \u2192 1\u00d710\u207b\u00b9\u2074), but hydrogen by only one order; hydrogen needs vacuum annealing or a long pump-down.<\/p>\n

How is a particle requirement converted to a per-wafer figure?<\/h3>\n

Through critical particle diameter against allowed defect count: the order of magnitude given by ITRS 2003 is 25\u201350 nm corresponding to 59\u201397 particles per wafer. Current thresholds are stricter \u2014 the customer specification governs.<\/p>\n","protected":false},"excerpt":{"rendered":"

Nine times out of ten the problem is outgassing, not leakage. Two sources dominate: water, and hydrogen trapped in the damaged surface layer. Baking and pumping time address the first; only the cleaning process addresses the second.<\/p>\n","protected":false},"author":1,"featured_media":121,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[8,6],"tags":[],"class_list":["post-98","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-en","category-clean-particle"],"_links":{"self":[{"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/posts\/98","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/comments?post=98"}],"version-history":[{"count":3,"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/posts\/98\/revisions"}],"predecessor-version":[{"id":153,"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/posts\/98\/revisions\/153"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/media\/121"}],"wp:attachment":[{"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/media?parent=98"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/categories?post=98"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/panovacuum.cn\/blog\/wp-json\/wp\/v2\/tags?post=98"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}